Portable printers are widely used in various applications such as home delivery services and inventory management. Such a portable printer is disclosed in, for example, JP-A-08-300740 (hereinafter referred to as Document 1). The portable printer disclosed in Document 1 stores a label sheet attached with a base sheet wound in a roll shape. The portable printer disclosed in Document 1 applies printing based on accumulated print data to labels stuck to the base sheet while drawing out the stored label sheet. As one form of use, the portable printer disclosed in Document 1 issues printed labels from an issue port together with the base sheet. In the portable printer, a line-type thermal print head configured to come into contact with a platen roller via a guide path for the label sheet performs printing.
Another form of use of the portable printer disclosed in Document 1 is peeling and issuance of printed labels. The portable printer disclosed in Document 1 includes a label peeling plate in the guide path for the label sheet. The label peeling plate is located further on a downstream side than the thermal print head. The label peeling plate bends the guide path. In the portable printer, a pinch roller is pressed against the platen roller via the bent guide path and the base sheet of the label sheet is conveyed by the platen roller and the pinch roller. The portable printer can peel off the labels from the base sheet using the bending of the base sheet by the label peeling plate and peel off printed labels from the base sheet and issue the printed labels.
A technique for pressing the pinch roller against the platen roller via the guide path bent by the label peeling plate and peeling and issuing printed labels is a technique widely adopted in the past as described in, for example, JP-A-11-171155.
When the pinch roller is pressed against the platen roller via the guide path bent by the label peeling plate and printed labels are peeled and issued, depending on a type of a label sheet, the printed labels cannot be normally peeled and issued. As an example, such a phenomenon occurs when a label sheet having relatively strong adhesiveness of labels on a base sheet is used. In such a label sheet, it is difficult to peel off the labels from the base sheet. Therefore, when base sheet conveying force by the platen roller and the pinch roller is insufficient, slip against the base sheet occurs in the pinch roller. Then, since the platen roller performs conveyance of the label sheet in a printing unit even while the slip against the base sheet occurs in the pinch roller, a label after printing is not peeled off from the base sheet and the slack of the label sheet occurs around the label peeling plate. In such a state, the portable printer cannot peel and issue the labels any more and, in some case, causes even a sheet jam.
In this case, if the pressing pressure of the pinch roller against the platen roller is set high, the pinch roller less easily slips against the base sheet. However, for the platen roller, the pressing pressure of the pinch roller is nothing but application of resistance. Therefore, if the pressing pressure of the pinch roller against the platen roller is set too high, this causes a fall in printing speed due to a fall in conveying speed of the label sheet. In particular, in a portable printer of a battery drive type, because there is limitation on a power supply capacity, the fall in the conveying speed of the label sheet tends to conspicuously occur. Therefore, if, by change, setting of an apparatus is adjusted to an exceptional label sheet having relatively strong adhesiveness of labels on a base sheet, a disadvantage is caused in that printing speed falls when other general standard label sheets are used. This is extremely inconvenient.